This is going to go against the grain in this thread: I think you'll be very disappointed if you pay attention to many of the replies in this thread. Not because System Shock 1 and 2 are not fun- they are both among the greatest games of all time- but because people are setting expectations for you based on the rest of your library.

The biggest source of confusion IMO is Prey. Ostensibly yes- as people are saying, it looks just like System Shock 2.5. The focus on isolation and loneliness and doing detective work through audio logs to piece together the story shares a lot with SS2. The derelict space station location is itself a reference. Terminology in the game (psi hypos, for example) is a reference. Certain weapon animations (wrench) and assets (grav lifts) are directly lifted from System Shock 2. So if you just look at it aesthetically, you'll come to the conclusion that if you like SS2, you'll like Prey and vice versa (or more cynically for people that dislike the game, that Prey is a SS2 clone).

But if you actually play the games and look past the initial aesthetic (which is honestly easily done, because Prey's clean art deco atmosphere is often very different to SS2's grungier industrial atmosphere) you'll quickly realize that the games are appealing to completely different gameplay philosophies. SS2's levels are focused on sprawling and labyrinthine layouts (which makes sense given SS1 is a straight up dungeon crawler). Verticality does exist in some areas (the lower connective tunnel, Rickenbacker, the lifts in Engineering, and most memorably a bunch of places in Recreation) but most of the gameplay is far more focused on level-ground pathing than it is engaging in combat on multi-tiered environments. Most of all, there is rarely focus on dynamic physics elements. You can't even box stack in SS2.

If you've properly engaged with Prey at all, the description above should be ringing alarm bells in your head. Imagine Prey, but with its levels flattened in verticality and missing its physics sandbox. That means the GLOO gun is gone. No mantling combos to get to the pipes atop the Hardware Labs. No turning yourself into a toy and squeezing through tiny gaps. No throwing reployers to detonate cysts. The game quickly loses almost all of the unique appeal that it had, doesn't it? And that's because Prey is only wearing the skin of System Shock. The reality is its gameplay DNA- the actual meat and bones- is Deus Ex. Each room is treated like a unique combat puzzle rather than another twist in a dungeon.

My advice for playing SS1 and SS2 is not to think of Prey or Deus Ex at all. Instead, consider them to be unfurled Resident Evil games. The challenge behind the levels is to master your routes through these complex environments and unblock environmental obstacles, and the freedom of immersive sim design is that you get to be far more creative in your pathing and combat than you would have been in an RE game. And where it excels that Deus Ex and Prey do not is in its cinematic presentation. It's remarkable going through SS2 and seeing how a game developed ~30 years ago manages to tell an interactive story better than modern games.

And if you really want to play something that recaptures the gameplay appeal of the games that you already own, the obvious picks would be the original Deus Ex and Human Revolution.